Does anyone know if the CAT 3208 diesel pusher buses use a secondary lift pump to get diesel to the IP? I can't seem to find anyother pump other than the manual primer pump. I suspect the primer just gets the fuel up to the IP and then the IP's internal transfer pump pulls the diesel from the tank, assuming no air is in the lines.

are you not getting fuel to the ip?
the common problem with 3208 is that the shaft seal in the ip leaks air back into the system whilst it is not running, you can tell if the seal is bad if there is diesel in the engine valley. the diagnosis is that, and also that the bus will run fine if primed or using starter fluid, but wont start cause no fuel is in ip.
if that is the case, the parts are very cheap. but r/r of ip is lotsa work.

mine leaks a little, so it's good for longer, i think its best just to replace the ip and maybe put in new injectors when the the fuel ip problem needs addressed.